In order to maintain, or even increase, the pressure at increased extraction rates, it has been known, for instance, to install butterfly valves designed to be controllable accordingly in the crossovers between the intermediate-pressure and low-pressure sections. A drawback has been in the fact that throttling by the valves is associated with a loss of pressure drop which involves a loss of electrical output.
In order to avoid the aforementioned drawback it has been known in district-heating power stations to provide pivotable guide vanes downstream of the steam extraction point and arrange to be pivoted by means of a device--such a control device was disclosed, for instance, by the German Preliminary Pat. No. 25 13 581, but there were no definite instructions in that disclosure regarding the means for the axial displacement of the adjusting ring connected to the adjusting arms.
As far as the applicant is aware of, the practical realization of adjustable guide vanes in large extraction (pass-out) condensing turbines failed because the adjusting devices in the interior of multi-casing turbines proved to be too complicated and mostly relied on oil-hydraulic actuating means. However, the use of oil is problematic because, in view of the fire risk, the oil has to be kept away from the hot steam.
The present invention has for its object to simplify a device of the type initially referred to in a manner that it can be applied primarily as an internal control device; furthermore, a fluid power type actuator is proposed to be used whose pressure fluid is well compatible with the working fluid used in the turbine.